Activated carbons have been used since World War I as an adsorbent to remove poisonous contaminants, principally cyanogen chloride, from air or other gases containing the poisonous contaminant. It has been used principally in gas masks to provide protection against chemical warfare agents, such as cyanogen chloride (CK) and chloropicrin (PS). Numerous toxic gases and liquids are used as chemical warfare agents. In testing the desirability of a particular carbon, cyanogen chloride is generally used as a test gas because the presence and effects of moisture greatly influence the ability of the carbon to remove this gas. Chloropicirin is selected as an additional test gas to measure the physical adsorption capacity of the carbon. The principal carbon used was a whetlerite carbon, a copper-treated carbon adapted to serve as an adsorbent for poisonous gas, and named after the first inventors, Joshua C. Whetzell and E. W. Fuller.
Additional metals have been impregnated in activated carbon to improve on its adsorption capabilities; e.g. ASC Whetlerite carbon, a copper, silver and chromium impregnated carbon. Cyanogen chloride removal is enhanced significantly by the copper and chromium impregnants in the ASC Whetlerite carbon. The cyanogen chloride, in part, reacts with the metal impregnant. On the other hand, some toxic gases, such as chloropicrin, are removed primarily by adsorption on the carbon pore surface, rather than by reaction with the metal impregnants. The available carbon pore surface (i.e. adsorption capacity) is, however, reduced by the added impregnants. Therefore, a good Whetlerite carbon product must have a careful balance of metal impregnant versus available pore surface. One of the principal drawbacks of ASC Whetlerite carbon is the deterioration of the cyanogen chloride removal caused by aging, which is defined as the equilibration over time of the carbon or impregnants with moisture picked up by the carbon.
More recently, organic compounds have been added to the ASC Whetlerite carbon, for example pyridine, picoline and triethylene diamine (TEDA) to reduce the aging effect. Since pyridine and picoline are liquids at room temperature, they are easily added to the carbon. TEDA, on the other hand, is a solid at room temperature and due to its limited solubility, has generally been added as an aqueous solution. Triethylene diamine impregnated ASC Whetlerite carbon has the advantage that it will, however, maintain its capacity to remove cyanogen chloride, in particular after aging, better than the pyridine or picoline impregnated carbons.
The instant invention is directed to an improved method of impregnating carbons with solid compounds, such as TEDA. The impregnated carbons of the instant invention have the capacity to remove cyanogen chloride over a longer period than prior art carbons. This has been accomplished by using triethylene diamine or other amine compounds which are solid and adding them to the carbon by sublimation, rather than as an aqueous solution. Since water is not added along with the TEDA, more adsorption capacity is retained for physical adsorption.